Inhibiting corrosion of copper and copper-base alloys



United States Patent Office Patented Jan. 3, 1967 r 3,295,917 INHIBITINGiCORROSION OF COPPER AND COPljER-BASE ALLOYS Joseph {Bernard Cotton, Little Aston, Sutton Coldiield,

England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed July.12, 1965, Ser. No. 471,423

Claims priority, application Great Britain, Dec. 4, 1959,

41,245/59; Apr. 27, 1961, 15,270/61 2 Claims; 01. 21-2.s

This application is a -continuation-in-part of Serial No. 73,224, filed December 2, 1960, now abandoned, and Serial No. 188,556,, filed April 18, 1962, now abandoned.

This invention relates to methods for inhibiting the corrosion of copper and copper containing alloys (hereinafter: referred to collectively as copper).

It is well known thatcopper is subject to corrosion, for example, ,in the form of staining or tarnishing, possibly due to the presence of moisture in air which is in contact with the copper during storage, use or transit. Corrosion isespecially likely to occur when the copper is exposed to certain types of solutions or atmospheres having high humidity.

Numerous prior proposals have been made for the purpose of obviating the abovementioned problem of copper corrosion. For example, it has been proposed to add one or more corrosion inhibitors to the environment which contactsthe copper, such as the coolant in vehicle radiators: or-thej fluid in hydraulic systems. However, this has made it necessary to provide a reservoir of the inhibitor in, the environment. For example, a supply of inhibitor must always be available in the coolant in the radiator of a vehicle ,',if the treatment is to be effective. This has the obvious, disadvantage that a fresh supply of inhibitor is necessary, Whenever the coolant is replenished. Domestic water systems also present serious corrosion problems. ItH is common practice to construct cylinders, tanks and pipe-Work for domestic water systems from copper or copper-base alloys but certain domestic water supplies are known to induce pitting corrosion in these materials. This corrosion is most prevalent in crevices, areas adjacent to constructional welds and at water-lines, especially in closed vessels. Consequently, considerable effort has been put into attempting to reduce the effect by careful design. i However, certain water supplies may induce pitting corrosion even in well designed systems having a minimum of crevices; welds, etc., and it is thought that corrosion under these t-circumstances may be due to the formation of discontinuous scale deposits or of certain types of oxide film on the inner surfaces of the water systems. In any event, attempts to prevent this form of corrosion have hitherto :been unsuccessful. One or more corrosion inhibitors could be added to the water in the system but this presents the disadvantage noted above, namely, the necessity for providing a reservoir or continuous supply of, the inhibitor.

Aswill be appreciated from the foregoing, there is a real1need in the art for inhibiting the corrosion of cop- 138121 The principal object of the present invention is to provide .novel methods of inhibiting copper corrosion whereby prior art difficulties are obviated. A more specific, object; of the invention is to provide methods of ,,.ment is carried out. Other objects will also be hereinafter H treating copper for the purpose of inhibiting corrosion whereby the inhibition remains effective after the opper has been removed from the medium in which the treatapparent from the description of the invention which follows.

Broadly stated, the methods of the invention involve treating the copper with a supply of benzotriazole vapor for a time sufficient to form a thin self-sustaining protec tive film or coating on the copper after which the copper is removed from the treating environment and utilized as desired. The success of the invention is based, in large measure, on the finding that by utilizing suitable conditions of application, a self-sustaining film of benzotriazole can be deposited on the copper with the result that the treated metal can be removed from the treating environment and stored, Worked or otherwise used as desired without corrosion. Benzotriazole has previously been proposed to inhibit corrosion of copper but in these prior proposals, the inhibiting effect has only been obtained by maintaining the copper in contact with the treating environment and the conditions employed have not been adequate to form a self-sustaining protective film. Thus, for example, Hatch 2,941,953 describes the addition of small amounts of benzotriazole to a water system in order to avoid corrosion of copper in contact therewith. However, when the supply of benzotriazole is discontinued or the copper is removed from the system, the copper can still corrode just as in the case of copper which has not been subjected to the action of benzotriazole. The same is true in the case where copper articles are wrapped or packaged in paper or paper board which has been impregnated with benzotriazole to inhibit corrosion. This type of treatment is only effective as long as the copper articles remain wrapped or packaged in the impregnated paper or equivalent so that the copper contacts the paper and/or benzotriazole vapors liberated therefrom. Thus, once the copper articles are removed from their wrapped or packaged environment, they are still subject to corrosion. This difliculty is obviated in the present invention by providing, as noted, a film of benzotriazole on the treated articles which is self-sustaining and remains thereon to preclude corrosion long after the articles have been removed from the benzotriazole vapors or solution treating environment.

In one embodiment of the invention, the self-sustaining corrosion inhibiting film of benzotriazole is formed by placing the copper in an atmosphere of benzotriazole vapor and the film formed by condensation of vapor on the metal surface. Advantageously, the metal is chilled, e.g. with a blast of air, to facilitate the vapor condensation and film formation. The temperature of the vapor and the temperature of the chilled metal, may be C. to C. and 0 C. to 15 C., respectively. A time of treatment of 5 to 15 minutes is usually adequate for present purposes and the atmosphere employed should preferably contain from 0.03 to 0.7 milligram of benzotriazole per liter.

It is desirable that the metal should be free of grease and oxide prior to the benzotriazole treatment. This may be conveniently accomplished by degreasing and/ or pickling the metal in an acid bath.

The treated surface is unaffected by moderate handling and it has been found that strip coated in this way may be subjected to as much as rolling reduction without the protection against corrosion becoming impaired.

Thus, copper strip or wire may be given an inte-raprocess treatment with benzotriazole so that it will remain bright and uncorroded until it is required for the next process, even though this may involve a delay of as much as several weeks. In processes which involve the use of lubricants which may have :a corrosive effect on the copper, it is possible to add benzotriazole to the lubricant so as to overcome the said effect and at the same time impart a considerable degree of lasting protection.

The following specific example illustrates the invention:

Example 1 A set of experiments was carried out using benzotriazole condensed from the vapor onto the sheet, this being achieved by chilling a sample sheet in an air blast after degreasing in trichloroethylene and then suspending the sample in an atmosphere saturated with benzotriazole maintained at about 85 C. The corrosion properties of the thus processed sheet were compared with those of a control sheet which was not treated with benzotr-iazole.

In the following tabulated results, the words As rolled and Vapor treated in the first column headed Conditions in Experiment refer to the absence or presence of benzotriazole coating on the metal. In the second column headed Conditions of Experiment, the reference to Alternating temperature is used to indicate that the sample was subjected to a humid atmosphere with the temperature fluctuating between hot and cold. The results Having described the invention what is claimed is:

1. A method of inhibiting the corrosion of copper by forming thereon a self-sustaining protective film, which comprises providing an atmosphere of benzotriazole vapor at a temperature of at least 75 C., placing the copper in said atmosphere at a temperature below the condensation point of said benzotriazole vapor, maintaining the copper in said atmosphere until a self-sustaining protective film is formed thereon and then removing the copper from said atmosphere.

2. The method of claim 1 wherein the copper is degreased and chilled to a temperature between 0 C. and 15 C. before it is placed in said atmosphere of hemetriazole vapor and said atmosphere contains from 0.03 to 0.7 milligram of benzotriazole per liter, said copper being maintained in said atmosphere for 5 to .15 minutes.

References Cited by the Examiner UNITED STATES PATENTS 2,618,606 11/1952 Schaeffer 252l37 2,643,177 6/1953 Wachter et a1. 252394 X 2,803,603 8/1957 Meighen 252-389 X 2,877,188 3/1959 Lid-dell 252389 2,941,953 6/1960 Hatch 212.5 X

FOREIGN PATENTS 967,086 8/1964 Great Britain.

OTHER REFERENCES Hackhs Chemical Dictionary, Third ed. (1944) (page 118).

MORRIS O. WOLK, Primary Examiner.

are given in terms of the degree of staining of the samples. J. ZATARGA, I. SCOVRONEK, Assistant Examiners.

Experiment Material Conditions in Duration of Conditions of Staining Experiment Experiment Experiment 1. Copper As rolled 10 days Alternating Tem- Severe.

perature 2. Copper Vapor treated." (1 Some samples slight,

others none. 3. Brass As rolled Moderate to severe. 4. Brass Vapor treated do do Very slight- 

1. A METHOD OF INHIBITING THE CORROSION OF COPPER BY FORMING THEREON A SELF-SUSTAINING PROTECTIVE FILM, WHICH COMPRISES PROVIDING AN ATMOSPHERE OF BENZOTRIAZOLE VAPOR AT A TEMPERATURE OF AT LEAST 75*C., PLACING THE COPPER IN SAID ATMOSPHERE AT A TEMPERATURE BELOW THE CONDENSATION POINT OF SAID BENZOTRIAZOLE VAPOR, MAINTAINING THE COPPER IN SAID ATMOSPHERE UNTIL A SELF-SUSTAINING PROTECTIVE FILM IS FORMED THEREON AND THEN REMOVING THE COPPER FROM SAID ATMOSPHERE. 